Allow focal length in main 3d view greater than 250mm

When sculpting realistic head(should I say portrait instead?), I have to set cameras around 2 meters away from the object to counter the fish eye distortion. When the auxiliary camera is only 2 meters away, it's possible to set the focal length to 250mm, which is allowed in the main 3d view. But when I want to check how the model looks by a distance of 4 meter or even 6 meters, I have to set up auxiliary cameras, which is very slow. And is I left the cameras "select able", the feature of "zoom with the depth of cursor to help determine how much the zooming effects" breaks hard. If I set the focal length of main 3d view to 250mm and try zoom out to have a correct distortion against the fish eye effection, then the model( the same size as a real human head, 20x20x20-ish cm) is only about 5cm big on my 24 inch monitor. Which pulls my head into the screen.. According to my test, a camera 6 meters away needs 880mm for the focal length. A camera 4 meters away needs 600mm. So, the suggestion is that, allow the focal length to reach 6000mm(or at least 2500mm) in main 3d view. (Now its max value is 250mm).